reverb unit HUUUMMMMMMM!

[dayn]

Just got a used reverb unit. Tubes are properly seated, connections seem fine, but when plugged into it and then into my amp, there is a really loud hum.



Goes away when I turn down the "return" knob on the reverb unit. Is this a ground loop or something else?

[xtian]

I have this problem with my Mesa Boogie Mk IV. Interested in general troubleshooting tips.

[dayn]

Just to be clear, this is an outboard reverb unit, that is between my guitar and amp like a pedal would be.

[selloutrr]

both the amp and the reverb unit are plugged into the same power source? i.e. power strip?

have you tried lifting the ground on one unit (probably the reverb) to test for ground loops?

Do you know the tubes in the reverb unit are GOOD?
Are the other components good... Filter Caps?, pots, etc.

The cables you are using have been tested for continuity and Ohm load?

Your plugging into the correct jacks? they are not reversed?

Guitar - Cable - Amp -(Send) - Cable - Reverb IN (Guitar) - Reverb Out (Amp)- Cable - Amp (Return)

_or_

Guitar - Cable - Reverb IN (Guitar) - Reverb Out (Amp)- Cable - Amp

[dayn]

Guitar, cable, reverb in, reverb out, amp

Have not tested tubes, but this is a JMI reverb/top boost unit and top boost portion is fine, reverb sounds fine too but hums when "return" knob is on (no reverb signal when it is off which is expected, but then also no noise).

Have not tested for ground lift (going to buy ground lift adapter to try this).

The unit is only 2 years old with light use so I "assume" not tubes or caps, etc, but ground loop. Once I answer that question, I can try tube swapping.

I tried plugging into same power outlet, as well as seperate outlets in the house on different circuits, same problem.

[angelodp]

I had a similar issue on a Rocket build which cleared up after I re-routed the reverb terminal grounds to the preamp grounds and isolated the terminal from the chassis. You might have a loop.

+1 on tubes. Put some known good tubes in first.


Ange

[tubeswell]

You probably need to re-do the reverb unit grounding to something like R.J. Keen's star grounding. I've done this in a 6G15 clone and its dead quiet. (BTW It is not a good idea to lift the chassis ground).

[dayn]

Why bad to lift ground? I mean specifically, not just might get a shock.k

[tubeswell]

Because then you rely on the unit's output cable shield to provide a safely grounded chassis, which it might do some of the time...

Its far safer to keep the chassis grounded with a properly attached mains chord, and instead focus on reducing the ground loops in the reverb unit and in your main amp.

[butwhatif]

Boogies' reverbs hum, I have done everything to mine and it's pretty good, and the pan is also flipped over, and backwards in the cabinet. The pan comes factory star grounded. I have been meaning to experiment w/ winding a humbucking return coil, an idea decades overdue---